42 terms

Meiosis (Reduction Division)

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Meiosis
A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
Homologous Chromosomes
Chromosomes that have a corresponding pair from the opposite sex parent.
Somatic Cells
Body cells.
Diploid
A cell that contains both sets of homologous chromosomes.
Autosome
A chromosome that is not a sex chromosome.
Haploid (Monoploid)
A cell that contains a single set of chromosomes.
Gamete
Sex cells (sperm & egg.)
Process of Meiosis
Starts with 1 diploid cell & ends with 4 haploid cells.
Product of Meiosis
A gamete.
Two Distinct Divisions
Meiosis 1 & Meiosis 2.
Interphase 1
Occurs before the cell enters meiosis. The cell grows, DNA is replicated & centrioles are replicated.
Prophase 1
DNA condenses from chromatin into chromosomes. The centrioles move to the poles & create the spindle. The nuclear membrane disintegrates & disappears. The nucleolus disintegrates & disappears. Each chromosome pairs with its corresponding chromosome to form a tetrad.
Tetrad
A group of four chromosomes that have crossed over.
Crossing Over
As homologous chromosomes pair up & form tetrads, they exchange portions of their chromatids. This results in an exchange of genes which produces new genetic combinations & genetic diversity.
Synapsis
Snap together.
Metaphase 1
The chromosomes line up double file in the middle of the cell. There are 2 chromosomes on each spindle fiber instead of only 1. Homologous pairs of chromosomes are located on each spindle fiber.
Anaphase 1
The centromeres of each chromosome does not disintegrate, so the sister chromatids do not separate. Entire chromosomes move to the poles- one chromosome in each pair goes to one side of the cell & the other chromosome in the pair goes to the other side.
Telophase 1
The chromosomes do not unwind back into chromatin. The spindle breaks apart & disappears. The nuclear membrane & nucleolus reform. Cytokinesis occurs. The cell separates into 2 cells.
Interphase 2
Between meiosis 1 & meiosis 2. DNA does not replicate.
Meiosis 2
The two cells produced by meiosis 1 enter a second meiotic division.
Prophase 2
DNA is already in chromosome form from meiosis 1. Centrioles move to the poles & create the spindle. The nuclear membrane & nucleolus disappear.
Metaphase 2
The chromosomes line up single file.
Anaphase 2
The centromere of each chromosome disintegrates & the sister chromatids separate- one chromatid goes to one pole & the other moves to the other pole.
Telophase 2
The chromosomes unwind back into chromatin. The spindle breaks apart & disappears. The nuclear membrane & nucleolus reforms. Cytokinesis occurs.
Nondisjunction
An uneven split in chromosomes (3:1) that can result in many different diseases.
Down Syndrome
A result of a chromosome imbalance.
What happens to DNA during Prophase I
DNA condenses from chromatin into chromosomes.
What happens to centrioles during Prophase I
The centrioles move to the poles & create the spindle.
What happens to the nuclear membrane & nucleolus during Prophase 1
They disintegrate.
How a tetrad is formed
Each chromosome pairs with its corresponding chromosome.
When synapsis occurs
During Prophase 1 when the chromosomes cross over & 'snap' together.
How chromosomes line up during Metaphase 1
Double file.
The number of chromosomes on each spindle fiber during Metaphase 1
2.
The type of pairs located on each spindle fiber
Homologous.
What happens to each centromere of chromosomes during Anaphase 1
They do not disintegrate & therefore, the sister chromatids do not separate.
How the chromosomes move to the poles during Anaphase 1
Entire chromosomes move to the poles- one chromosome in each pair goes to one side of the cell & the other chromosome in the pair goes to the other side.
What happens to chromosomes during Telophase 1
The chromosomes do not unwind back into chromatin.
What happens to DNA during Interphase 2
DNA does not replicate.
What happens to the nuclear membrane & nucleolus during Prophase 2
They disintegrate.
How chromosomes line up during Metaphase 2
Single file.
What separates during Anaphase 2
The sister chromatids separate- one chromatid goes to one pole & the other moves to the other pole.
What happens to chromosomes during Telophase 2
The chromosomes unwind back into chromatin.